MORPHOLOGY OF TEOSINTOID AND TRIPSACOID MAIZE (ZEA MAYS L.)

Modern races of maize (Zea mays L.) are characterized by indurated glume and rachis tissues. The archaeological record, as well as experimental studies indicate that in North America this induration is associated with hybridization between domesticated maize and its closest wild relative Z. mays subsp. mexicana (Schrad.) Iltis (teosinte). Similar induration can also be introduced into maize through introgression from Tripsacum. North and South American indurated races of maize are not all closely allied morphologically. They evolved independently under domestication. Teosinte is absent from South America, but Tripsacum is widely sympatric with maize from about 42 N to 42 S latitude. For these reasons it has been postulated that induration in South American races may be the result of Tripsacum introgression. However, barriers restricting gene exchange between Zea and Tripsacum are difficult to overcome in nature. It is maintained that indurated South American races of maize were derived from indurated Mexican races, and that the presence or absence of such induration is due to different degrees of expression by intermediate alleles of the tunicate locus.